1. The Field of the Invention
The present invention relates to implantable prosthetic joint devices for application in the human body. More particularly the present invention is directed to a prosthetic device which can be readily assembled and disassembled in place so as to assure proper fit.
2. Description of the Prior Art
The pelvis in the human body contains two hip bones, one on each side of the body, each containing an acetabulum or hip socket for receiving and forming a seat for the femoral head or ball of the femoral or thigh bone. The femoral head is connected to the thigh bone by a neck which is angularly disposed relative to the axis of the femoral and relative to the vertical axis of the body. Thus any load applied by the body through the hip and femoral neck to the thigh bone and leg and any impact, such as caused by walking, jumping and the like applied by the leg and thigh bone through the femoral neck and hip to the body, is transmitted angularly through the femoral neck. This angular transmission of the load and forces through the femoral neck results in high stresses and high sheer-loads applied to the femoral neck. These high stresses, when normally applied can cause dislocation of the femoral head from the acetabulum or hip socket and fracture and breaking of the femoral neck. In older people such femoral neck often becomes brittle and in both older and younger people is subject to injury. Replacement is often required.
The utilization of prosthetic devices which are implanted into the human body for replacing defective, damaged or diseased joints of the type described above have been well known. One known specific form of prosthetic device is for use in replacing anatomical joints of the body having ball and socket characteristics, as for example the above-discussed hip joint. Such a prosthesis essentially provides a detachable inner-connection between the femoral and the acetabulum socket of the pelvis which serves the purpose of accomplishing the universal-type movement associated with the replaced natural biological joint. Conventional prosthetic hip joints normally embody an acetabulum-type cup member having a spherical cavity, which may be suitably secured in a variety of ways to the acetabulum pocket of the pelvis, and an artificial femoral head which is appropriately attached to the femoral. The femoral insert includes a smooth and substantially spherical head member which mates with and is rotatably supported by the spherical cavity of the cup member. As a result of this structural inner-relationship, a ball and socket-type joint is created which permits ordinary-type of articulated motion associated with the human hip joint.
In this particular field there are several known approaches for forming such artificial joints. Specific reference is made to U.S. Pat. Nos. 3,813,699; 4,044,403; 4,380,090; and 4,624,674. Each of these patents show and describes femoral heads and necks for surgical implants as replacements for damaged or broken natural heads or necks. In each such device an outer spherical metal cup having an inner plastic insert, is provided for implanting into the acetabulum or hip socket. The inner plastic insert has a socket into which the metal sphere, having a neck and a stem for connection to the thigh bone, is pivotally received.
While these devices have generally served their desired function, they have not been entirely without problems. One of the primary problems is in achieving the proper size combination of the prosthetic components so that the femoral head will regain its proper orientation with respect to the hip as a whole. In order to provide for size adjustment, the prosthetic device must be capable of being assembled in the operating room with a degree of facility and ease that has not been found in the previous devices, many of which are pre-assembled using fairly difficult assembly techniques. It is the intention of the '403 patent mentioned above, to provide a prosthesis which will result in a firm non-dislocatable joint. In contradistinction, the '463 patent has as its object to provide a prosthetic joint which, when dislocated by an unusual action, can be properly relocated by non-invasive techniques.